Plant protection products in the form of a granulate with controlled release of the active agent

ABSTRACT

Crop protection granules based on the active substance tetrahydro-3,5-dimethyl-1,3,5-thiadiazine-2-thione and comprising an outer shell having a proportion by weight of from 0.1 to 50% by weight, based on the granules, of which at least 50% by weight consists of sulfur or sulfur compounds.

The present invention relates to crop protection granules based on theactive substance tetrahydro-3,5-dimethyl-1,3,5-thiadiazine-2-thione.

U.S. Pat. No. 2,838,389 describes the use oftetrahydro-3,5-dimethyl-1,3,5-thiadiazine-2-thione of the formula (I),common name dazomet, as a soil decontaminant in agriculture andhorticulture.

For an end user incorporating dazomet into the soil by mechanical means,it is fundamentally of prime advantage to be able to use dust-freegranules.

A process for preparing such substantially dust-free granules isdescribed in EP A 618 912. By adding alkylenediamines of the generalformula R¹NH—A—NHR (III) (R and R¹ independently are hydrogen orC₁-C₄-alkyl and A is a 1,2-ethylene, 1,3-propylene or 1,4-butylenebridge) in the course of dazomet's preparation, control is exerted overcrystallization or granulation and so substantially dust-free dazometgranules are obtained with qualities advantageous to the end user.Corresponding products are obtainable commercially under the trade nameBasamid from BASF Aktiengesellschaft.

Forest Prod. J. 43(2): 41-44 (1993), Acta Horticulture 382 (1995) p. 110ff. and Food and Fiber Science, 27(2) 1995, pp. 183-197 and furtherreferences cited therein describe the use of dazomet granules and themode of action of the released product methyl isothiocyanate

CH₃—N═C═S  (II)

(MITC), which functions as the actual biologically active agent.Accordingly, dazomet itself can be regarded merely so to speak as aprodrug precursor.

Comparatively little is known even now about the nature and activationof the release of MITC from dazomet in the soil. The literature does,however, reveal that the soil pH, transition metals or, for example,soil moisture and soil temperature all have a part to play. This isconfirmed by our own studies.

The dazomet granules prepared in accordance with the abovementioned EP 0618 912, although being substantially dust-free, have but a very limitedinfluence over the release of MITC and are therefore unable to provide acompletely satisfactory solution to one application problem: the controlof active substance release, and especially the retarding thereof.

Thus it has been found when using such dazomet granules that, given highsoil temperatures of more than 30° C. and sufficient soil moisture, MITCis released very quickly and then when the granules are incorporatedinto the soil, especially in glasshouse applications, MITC may lead totemporary mucosae and eye irritations in the absence of properventilation and use.

It would therefore be desirable for this utility to retard the releaseof MITC to a sufficient degree to give the personnel charged withapplying the product sufficient time to leave the glasshouse before theactive substance is released.

An alternative soil decontaminant, gaseous methyl bromide, hasdisadvantages in terms of its known ozone harmfulness.

Metam fluid and metam-sodium are of only limited glasshouse utilityowing to their very rapid and strong propensity to evolve gas, or even,as for example in California, are no longer approved.

The “Montreal Protocol on Substances that deplete the Ozone Layer” inPart IV: Assessment of the Economic Viability of Methyl BromideAlternatives, April 1997 Report Vol. II cites on page 260 the use ofdazomet as a potential alternative for methyl bromide but points toproblems in its application by untrained users.

It is an object of the present invention to provide crop protectiongranules based on the active substancetetrahydro-3,5-dimethyl-3,5-thiadiazine-2-thione in which there isdelayed and/or controlled release of the active substance.

We have found that this object is achieved by crop protection granulesbased on the active substancetetrahydro-3,5-dimethyl-1,3,5-thiadiazine-2-thione which comprise anouter shell which makes up from 0.1 to 50% by weight of the overallweight of the granules and of which at least 50% by weight consists ofsulfur compounds or sulfur itself.

The subclaims and the subsequent description reveal preferredembodiments of the invention.

The invention additionally relates to a method of combating nematodes,soil-dwelling insects, germinating plants, soil bacteria and soil fungiby treating the soil with an effective amount of from 1 to 1000 kg/ha ofsoil surface of the granules of the invention.

The invention gives preference to dazomet granules as obtained by theprocess described in EP 618 912, i.e. to products in whose preparationfrom 0.1 to 10 mol % of diaminoalkylene compounds R¹NH—A—NHR (R, R¹ andA are as defined at the outset) are added. For further preparationdetails reference is made to EP 618 912.

The outer shell preferably makes up from 1 to 35 and, in particular,from 2 to 25% by weight of the granules.

Preferably from 55 to 100 and, with particular preference, from 75 to100% by weight of the shell consists of sulfur compounds or elementalsulfur.

A particularly preferred shell material is elemental sulfur, especiallythose products which can be employed in the form of aqueous dispersions.

Thus it has surprisingly been found that aqueous sulfur dispersions,such as aqueous redispersion concentrates of the commercial productKumulus® DF, are particularly suitable as shell constituents.

An advantage of using such shell materials is that they can be appliedto the dazomet granules by the fluidized bed technique without theoccurrence of disadvantages in processing, such as agglomeration,formation of coarse grains or disadvantages in terms of the abrasionbehavior.

Such sulfur dispersions are preferably prepared by one of the followingtechniques:

Technique A

Sulfur suspension concentrates by aqueous grinding techniques fromelemental sulfur with appropriate auxiliaries

Elemental sulfur, such as sulfur powder, is suspended in water,judiciously with the addition of wetting agents and dispersants and, ifdesired, with the addition of a binder. The still coarse sulfursuspension is then comminuted, preferably in plain or stirred ballmillswith grinding media—for example, glass grinding media or other mineralor metallic grinding media—having a size (average diameter) of ingeneral 0.1-30 mm, preferably 0.6-2 mm, until the average particle sizeis preferably less than 10 μm.

Technique B

Sulfur suspension concentrates from melt-spray sulfur granulesredispersed in water

Melt-spray sulfur granules are obtained by melting elemental sulfur,such as sulfur powder, by heating it to temperatures of more than 120°C. and spraying the resulting melt, directly or following the additionof wetting agents and dispersants, in an appropriate spraying device,such as in a spray tower, generally with cooling, to form the spraysulfur granules.

Examples of suitable wetting agents and dispersants for both techniquesare the following auxiliaries from the following classes of substance:

Fatty acid polyoxyethylene esters, such as lauryl alcoholpolyoxyethylene ether acetate,

alkyl polyoxyethylene or polyoxypropylene ethers, such as those ofisotridecyl alcohol, and fatty alcohol polyoxyethylene ethers,

alkylaryl alcohol polyoxyethylene ethers, such asoctylphenol-polyoxyethylene ether or tributylphenol polyoxyethyleneether,

ethoxylated isooctyl-, octyl- or nonylphenol or castor oil, sorbitolesters,

arylsulfonic acids, alkylsulfonic acids, alkylsulfuric acids or theiralkali metal, alkaline earth metal and ammonium salts, especially saltsof arylsulfonic acids, examples being lignin-, phenol-, naphthaline- anddibutylnaphthalinesulfonic acids,

alkylsulfonic acids, alkylarylsulfonic acids, alkylsulfuric, laurylether sulfuric and fatty alcohol sulfuric acids, fatty acids, sulfatedhexa-, hepta- and octadecanols and fatty alcohol glycol ethers,

condensates of sulfonated naphthaline and its derivatives withformaldehyde,

condensates of naphthalinesulfonic acids with phenol and formaldehyde,and

protein hydrolysates.

In addition, lignin sulfite waste liquors and methylcellulose are alsoparticularly suitable.

Examples which may be mentioned here are:

Benzenesulfonic acid and its C₁₀-C₁₆-alkylderivatives and also itssodium, potassium, calcium and magnesium salts, diisobutyl-,diisopropyl-and dimethylnaphthalinesulfonic acid and their corresponding sodium,potassium, calcium or magnesium salts, preferably the sodium salts,ammonium salts and sodium salts of the monoether of ethoxylateddodecanol with sulfuric acid, monoethers of ethoxylated dodecyl alcoholwith sulfuric acid, various salts of dodecyl sulfate (Na, K, Ca, Mg),salts of dodecylbenzenesulfonic acid with Na, K, Ca, triethanolamine ortriethylamine, ammonium or sodium salts of condensates ofnaphthalinesulfonic acid and formaldehyde, condensates of phenolsulfonicacid, urea and formaldehyde and salts thereof, xyloylsulfonic acid andits salts, and sodium salts of C₁₂-C₁₆ 2-alkenesulfonic acids.

The granules of the invention are preferably prepared in a fluidized bedunit. For this purpose the dazomet granules are then fluidized, and atthe same time a generally aqueous sulfur dispersion (where suchdispersions are used as shell materials), together if desired withfurther auxiliaries such as polymers, wetting agents or dispersants,emulsifiers or binders, is sprayed onto the granules of activesubstance.

Suitable auxiliaries and shell materials, which are sprayed onto thedazomet granules in mixtures, together or separately, with sulfurdispersions, include in particular the following binders: cellulosederivatives, such as cellulose esters, cellulose etherscarboxymethylcellulose, hydroxypropylmethylcellulose, water-solublegums, such as gum arabic, gum tragacanth, alginates, gelatins, modifiedstarches, such as sodium carboxymethyl starch, as auxiliaries fromnatural sources, and also cellulose, cellulose acetates, cellulosecarboxymethyl ether and its sodium salt, cellulose 2-hydroxypropyl etherand cellulose 2-hydroxyethyl ether, cellulose ethyl ether, celluloseethyl ether, and regenerated cellulose, to name but a few.

At least 50% by weight, preferably from 55 to 100% by weight, of theshell of the granules of the invention consists of sulfur or sulfurcompounds. In order to control the properties of the shell, and inparticular to control the release of MITC, it is also possible to use inaddition to sulfur and sulfur compounds, for example, polymeric shellsubstances in an amount of up to 45% by weight, preferably up to 40% byweight, based on the shell.

It is preferred to employ aqueous wax dispersions comprising, based onthe aqueous wax dispersion, from 5 to 40% by weight of an ethylenecopolymer wax, consisting of from 10 to 25% by weight of anα-olefinically unsaturated mono- or dicarboxylic acid having 3 to 8carbons and from 90 to 75% by weight of ethylene having an MFI, measuredat 190° C. and under a load of 2.16 kp, of from 1 to 600, preferablyfrom 5 to 500 and, in particular from 15 to 300, or having an MFI,measured at 160° C. and under 325 p, of from 1 to 600, from 0.1 to 5% byweight of alkali metal hydroxide, ammonia an alkanolamine or adialkanolamine and mixtures thereof, and, as the remainder, water to100%.

The copolymers of ethylene which are particularly suitable for waxdispersions contain from 10 to 25% by weight, preferably from 15 to 24%by weight, of α-olefinically unsaturated mono- or dicarboxylic acidshaving 3 to 8 carbons, of which examples that may be mentioned areacrylic, methacrylic, crotonic, maleic, fumaric and itaconic acid. Ofthese, methacrylic acid and especially acrylic acid and mixtures thereofare preferred.

The ethylene copolymer waxes are characterized by their MFI (Melt FlowIndex) or melt index. The MFI indicates the amount of the polymer melt,in grams, which can be pressed through a nozzle of defined dimensionsunder a defined application of force (load) at a certain temperature.The melt indices (MFI units) are determined in accordance with thefollowing standards: ASTM D 1238-65 T, ISO R 1133-1696 (E) or DIN 53 735(1970).

In addition, the wax dispersions preferably comprise bases, generally0.1-5, preferably from 1 to 3% by weight of alkali metal hydroxide,preferably sodium hydroxide or potassium hydroxide, ammonia, a mono-,di- or trialkanolamine having in each case 2 to 18 carbons in thehydroxyalkyl radical, preferably 2 to 6 carbons, or mixtures of saidalkanolamines, or a dialkylmonoalkanolamine having in each case 2 to 8carbons in the alkyl and hydroxyalkyl radicals, or mixtures thereof.Examples of amines are diethanolamine, triethanolamine,2-amino-2-methyl-1-propanol or dimethylethanolamine. Ammonia ispreferably used.

As a result of the base fraction in the wax dispersions, the carboxylgroups in the copolymer waxes are present at least in part in the saltform. Preferably, from 50 to 90% and, in particular, up to 60 to 85% ofthese groups are in neutralized form.

Particular preference is given to a wax dispersion which consists of orcomprises from 5 to 40% by weight of an ethylene copolymer wax, from 0.1to 5% by weight of ammonia and from 55 to 94.9% by weight of water, theethylene copolymer wax being composed of from 75 to 90% by weight ofethylene units and up to from 10 to 25% by weight of units of anα-olefinically unsaturated mono- or dicarboxylic acid having 3 to 8carbons.

Further examples of suitable polymeric shell materials are thefollowing:

copolymers of butyl acrylate, 2-hydroxyethyl methacrylate, methacrylicacid and styrene,

copolymers of butyl acrylate, 2-hydroxyethyl methacrylate, methylmethacrylate and styrene,

copolymers of butyl acrylate, butyl methacrylate, methacrylic aid andstyrene,

copolymers of butyl acrylate, hydroxyethyl acrylates andmethylmethacrylate,

copolymers of butyl methacrylate, 2-ethylhexyl acrylate and styrene

copolymers of butyl methacrylate, 2-hydroxyethyl methacrylate, methylmethacrylate and styrene,

copolymers of n-butyl methacrylate, 2-hydroxyethyl methacrylate, methylmethacrylate and styrene,

ethylene-vinyl acetate copolymers,

sodium and ammonium salts of ethylene-acrylic acid copolymers,

copolymers of methyl methacrylate and acrylic acid, butyl acrylate,butyl methacrylate or mixtures thereof,

polyvinyl acetate, polyvinyl ethers, polyacrylamides, polyamides,

polyvinyl alcohol, polyvinylpyrrolidone,

polyvinylpyrrolidone-vinyl acetate copolymers,

copolymers of vinyl acetate with methyl acrylate, methyl methacrylate,butyl acrylate and acrylic acid or mixtures thereof, copolymers ofvinylpyrrolidones with long-chain 1-alkenes, and copolymers of crotonicacid, vinyl acetate and vinyl propionate.

The shell layer may also comprise substances for controlling the releaseof the active substances. Examples are water-soluble substances such aspolyethylene glycols, polyvinylpyrrolidone and copolymers ofpolyvinylpyrrolidone and polyvinyl acetate. The amount thereof is forexample from 0.1 to 5% by weight, preferably from 0.1 to 3% by weight,based on the shell substance.

The above-described shell polymers are general knowledge or areobtainable by known methods (cf. e.g. DE-A 34 20 168; EP-A 201 702; U.S.Pat. No. 206 279).

Such shell layers are judiciously applied by spray application ofsolutions, dispersions or dispersion of said shell substances togetherwith the sulfur or the sulfur compound in organic solvents or water.

It is preferred to use an aqueous suspension or an emulsion of the shellsubstance having, in particular, a content of polymer substance of from0.1 to 50% by weight, in particular, from 1 to 35% by weight. In thiscase, further auxiliaries may also be added in order to optimizeprocessing, examples being surfactants and solids such as talc and/ormagnesium stearate.

The wax dispersions described above can also be applied together withsulfur dispersions and/or other auxiliaries to the dazomet granules byspray application in the fluidized bed technique.

With granules provided in accordance with the invention with an outershell, MITC release is retarded significantly in comparison with thecustomary commercial products, especially at high temperatures, withouta significant increase in the duration of the dissipation phasefollowing treatment; in other words, the MITC mineralization requiredbefore resowing can begin takes place within virtually the same periodof time as with the known products. This represents a significanttechnical advantage.

The crop protection granules of the invention may also include otheractive substances or may be applied together with other compositionstogether in unison, mixed or separately in succession. The proportion ofthe further active substances is preferably up to 20% by weight, inparticular up to 10% by weight, based on the overall weight. Suitablefurther compositions are known per se to the skilled worker and aredescribed in the literature, so that further details are unnecessaryhere.

EXAMPLES Example 1 Preparing Melt-spray Sulfur Granules with SubsequentRedispersion in Water

Sulfur powder was heated to a temperature of more than 120° C. andmelted. The melt was mixed with sodium ligninsulfonate as wetting agentand silica as dispersant. The melt mixture was sprayed in a spray towerusing a dual-substance nozzle. This gave readily dispersible spraygranules (particle diameter: 60<x<300 μm), containing 0.3% by weight ofdispersant and about 20% by weight of wetting agent. The remainder wassulfur. The melt-spray granules obtained were then dispersed in an equalamount of water and the dispersion was then processed further inaccordance with Example 3.

Example 2 Preparing a Sulfur Suspension by Aqueous-mechanical FineGrinding in Stirred Mills

Sulfur powder was suspended in water, and sodium ligninsulfonate isadded as dispersant. Nonylphenol polyethoxylate was also added as awetting agent. The suspension was adjusted to a pumpable concentration;a sulfur concentration of 50% by weight was judicious.

To form a sprayable suspension the batch was ground in a laboratorystirred mill until a particle distribution of 40%<2 micrometers wasobtained.

Based on the total dry mass, the proportion of the sulfur was 80% byweight, the concentration of the sodium ligninsulfonate in the examplewas 19% by weight and that of the wetting agent was 1% by weight. Theaddition of an antifoam, such as silicone SRE in a concentration of upto 0.1%, suppressed the formation of foam in the course of milling.

Example 3 Preparing the Dazomet Granules of the Invention

2 kg of granules prepared in accordance with EP 0 618 912 wereintroduced into a spray fluidized bed.

A 50% aqueous suspension of sulfur was then sprayed onto these carriergranules in the course of 20 minutes. The dazomet granules during thistime were fluidized with an air quantity of 130 m³/h. The aqueous sulfursuspension is sprayed on at a pressure of 1.5 bar.

The following samples were prepared by the method described above:

TABLE 1 Proportion by weight of the outer shell and its Sample No.composition 1 no shell (control sample) 2 10% of S granules as in Ex. 33 20% of S-granules as in Ex. 3 4 10% of S-granules as in Ex. 3 + 5% ofpolymer 1 5 5% of S granules as in Ex. 3 + 5% of polymer 2

The polymer 1 employed in sample 4 is a wax dispersion in accordancewith Example 1 of EP 734,205; the polymer 2 employed in sample 5 wassodium salt of a phenolsulfonic acid/formaldehyde/urea condensate.

MITC release was determined by the following method:

400 g of dried and non-lumpy soil (pH 7.9 Limburgerhof site) were mixedthoroughly with 160 mg of samples 1 to 5, wetted with 50 ml of water andplaced in a test vessel (glass, internal diameter of 100 mm, gas space300 ml), which was then sealed and placed in a climatically controlledcabinet. 10 ml/min of purified air were passed through the vessel. Onleaving the vessel, this air was passed directly through a heatedconnecting line into the flame ionization detector (FID) of a gaschromatograph. The detector signal corresponds virtually 100% to theorganic carbon content of the measured gas. Other than methylisocyanate, virtually no further FID-detectable compounds or volatilegases are generally found with dazomet breakdown. Calibration was doneusing a calibrating gas (propane in nitrogen) with account being takenof a substance-specific correction factor.

The results of the experiments are set out in Table 2 below.

TABLE 2 Sample Sample Sample Sample Sample Sample Sample 1 1 1 2 3 4 5Conc. Conc. Conc. Conc. Conc. Conc. Conc. Measurement period MITC MITCMITC MITC MITC MITC MITC in h mg/m³ mg/m³ mg/m³ mg/m³ mg/m³ mg/m³ mg/m³0.5 110 361 550 220 110 110 220 1 220 723 1210 660 440 165 770 2 3031627 3080 1980 1870 440 2420 6 743 3795 8030 4620 5060 1705 5940 12 13204389 5280 3740 4070 2585 4620 18 1678 3589 3080 2640 2640 2585 2915 241859 2556 1760 1760 1650 2145 1815 Temp./ 15 25 35 35 35 35 35 ° C.

The results of the experiments carried out show that in all cases theenvelopment in a shell achieves a significantly retarded release of MITCat 35° C. The rate of release corresponds approximately to that of thegranules without a shell at 15° C. It is advantageous and surprising,especially in the case of sample 4, that just 6 h afterincorporation—this corresponds roughly to practice—a higher rate ofrelease is obtained than in the case of granules without a shell at 15°C. This is a desirable effect, since a faster rate of MITC dissipationis achieved thereby, despite the initially delayed release, and hence anearlier resowing date is possible in the case of new planting.

A further positive effect is that at the application rates of thedazomet granules, which lie preferably within the range from 1 to 1000kg/ha, with particular preference from 10 to 800 and, in particular,from 100 to 600 kg/ha of soil surface, significant amounts of sulfur areintroduced into the soil, which by virtue of fertilization effects areto the long-term good of the plant growth.

Moreover, an additional fungicidal, nematicidal or insecticidal effectis anticipated by virtue of the sulfur.

What is claimed is:
 1. Crop protection granules comprising a core oftetrahydro-3,5-dimethyl-1,3,5-thiadiazine-2-thione as an activesubstance and an outer shell, the proportion of the outer shell beingfrom 0.1 to 50% by weight, based on the weight of the entire granules,wherein at least 50% by weight of the shell consists of elementalsulfur.
 2. The crop protection granules of claim 1, wherein sulfur inthe form of a suspension concentrate is the starting material for theouter shell.
 3. The crop protection granules of claim 1, wherein theactive substance present has been prepared with the addition of from 0.1to 10 mol % of diaminoalkylene compounds of formula IIIR¹NH—A—NHR  (III) where R and R¹ independently are hydrogen or aC₁-C₄-alkyl group and A is a 1,2-ethylene, 1,3-propylene or 1,4-butylenebridge.
 4. A method of combating nematodes, soil-dwelling insects,germinating plants, soil bacteria and soil fungi, which comprisestreating the soil with an amount of from 1 to 1000 kg/ha of soil surfaceof the crop protection granules of claim
 1. 5. A process for preparingcrop protection granules as defined in claim 1, which comprises (a)fluidizing granules of the active substancetetrahydro-3,5-dimethyl-1,3,5-thiadiazine-2-thione by a fluidized edtechnique and (b) coating the fluidized granules from (a) with anaqueous suspension of the shell material.
 6. Crop protection granules asclaimed in claim 1, wherein from 55 to 100% of the outer shell iselemental sulfur.
 7. Crop protection granules as claimed in claim 1,wherein from 75 to 100% of the outer shell is elemental sulfur.
 8. Cropprotection granules as claimed in claim 1, wherein the outer shellconstitutes from 1 to 35% by weight of the granules.
 9. Crop protectiongranules as claimed in claim 1, wherein the outer shell constitutes from2 to 25% by weight of the granules.